This invention relates to an improved method for preparing a glare-reducing image transmitting lithium-silicate coating on a glass support, such as a viewing surface of a cathode-ray tube, CRT. The coating also may be formulated to provide antistatic characteristics.
S. B. Deal et al. U.S. Pat. No. 4,560,581, issued on Dec., 24, 1985, describes a method for preparing a lithium-silicate, glare reducing coating on a glass support. In that prior method, the glass support is warmed, to about 40.degree. to 80.degree. C., and then coated, e.g., by air spraying, with a dilute aqueous solution containing a lithium-stabilized silica sol. The coating is air dried, washed with warm water, air dried a second time, and then baked at a temperature below 100.degree. C., and preferably at about 90.degree. C., for 10 to 60 minutes. The abrasion resistance is directly related to the baking temperature. The higher the baking temperature the higher will be the abrasion resistance of the coating. The process differs from the processes disclosed previously in M. G. Brown, Jr. et al., U.S. Pat. No. 3,898,509, issued on Aug. 5, 1975, and S. B. Deal et al., U.S. Pat. No. 3,940,511, issued on Feb. 24, 1976, in that the methods disclosed in the latter mentioned patents require that the coating be baked dry at temperatures above 150.degree. C., before washing. The patentees believed the pre-wash high temperature bake was required to reduce the solubility of the coating in water, to increase its adherence to the glass support, and to increase its resistance to abrasion to practical values.
S. B. Deal et al., U.S. Pat. No. 4,563,612, issued, on Jan. 7, 1986, discloses a cathode-ray tube having, on its external viewing surface, an antistatic, glare-reducing image-transmitting coating. The coating composition includes, in addition to an aqueous lithium-stabilized silica sol, an inorganic metallic compound which imparts an antistatic characteristic to the coating. The coating is applied, e.g., by air spraying, to the tube faceplate which has been warmed to about 40.degree. to 45.degree. C., for about 30 minutes. The coating is dried and then baked at between 150.degree. and 300.degree. C. for 10 to 60 minutes; although, a 10 minute bake at a temperature of 120.degree. C. (with a 30 minute warm-up and 30 minute cool-down) has also been successfully utilized. The baking develops the final electrical, optical and physical properties of the antistatic, glare-reducing coating. The coating is disclosed to be inexpensive, easy to make, and more resistant to abrasion and to ordinary factory heat-treating operations than the structurally different quarter-wave glare-reducing coatings of the prior art which are said to have an antistatic characteristic.
A drawback of the antistatic, glare-reducing coating described in U.S. Pat. No. 4,563,612 is that a time consuming, costly baking step, at temperatures of at least 120.degree. C. and preferably in the range of 150.degree. to 300.degree. C., is used in order to develop the final electrical, optical and physical properties of the coating.